Most films I can think of that have been split into two parts are based on a single literary source (Potter, Twilight, Hunger Games, The Hobbit) which is fairly well known to the public and has a big fanbase.

Would there be the same excitmenet to see the second part of an X-Men story?

__________________Show me an X-Men comic where Mystique is the leader and walks round all day as a bored blonde